IB has always been a pain when it comes to either depositing checks or remitting checks. This is done, in my guess, to encourage all of their clients to use wire transfers exclusively. For future reference, never do anything by check with IB. Do not request checks, nor fund your account with checks. Use only wire transfers...

The policy has to do with bad checks and reducing fraud. If you send a bank check (the types accepted are listed on the site), they will be credited within 1 day within input into the system. Any type of check that has a possibility of bouncing is subject to a delayed credit.